Ultra-Circular Population Report
A systematic archival sweep of the JPL Small-Body Database for near-Earth asteroids on nearly circular, low-inclination orbits reveals 29 objects at a = 0.97–1.03 AU with no analog at any other semi-major axis zone in the inner solar system. None of the twenty-nine have any physical characterization — no spectrum, no albedo, no rotation period, no diameter measurement. The population is orbitally anomalous and physically unknown.
The question carried into this inquiry was narrow and instrumental. Across the set of near-Earth asteroids, is there a subset whose orbital geometry departs from what natural delivery mechanisms typically produce, and which has never been examined closely enough to say what it is? We asked the catalogue and the catalogue answered with a number.
Background
Near-Earth asteroids are supplied primarily by Yarkovsky drift out of the main belt through mean-motion and secular resonances (Granvik et al. 2018). The process delivers objects at eccentricities around 0.2–0.5 and inclinations around 10–20°. An object sitting in a near-perfect circle at 1 AU, tipped barely off the ecliptic, is not what this pipeline produces. It must have been captured into Earth's 1:1 mean-motion resonance and slowly circularized, injected directly at very low relative velocity (lunar ejecta, for instance), or arrived by a process outside the standard model. The selection filter we applied — e < 0.05, i < 5° — is therefore not arbitrary. It isolates the dynamically unlikely.
Discovery bias works further against finding these objects. Bodies on Earth-like orbits spend most of their time at large solar elongation, faint and slow-moving against the stellar field. They surface only during brief close-approach windows. Whatever the observed count turns out to be, it is almost certainly an undercount of the population actually present.
Sample construction
The JPL SBDB was queried across five semi-major axis zones spanning the inner solar system — inner (0.50–0.70 AU), Venus (0.70–0.76 AU), Earth (0.97–1.03 AU), outer (1.10–1.30 AU), and Mars (1.30–1.36 AU). Within each zone we selected only those NEAs with e < 0.05 and i < 5°. The query is fully reproducible; nothing interpretive enters the sample.
Results
The Earth zone contains 29 ultra-circular objects — 2.70% of its population. The Venus, Mars, and inner zones combined contain 2,020 objects and zero ultra-circular members. The outer zone (1.10–1.30 AU, possibly reflecting Mars's 1:1 resonance) contains 12 ultra-circular objects at 0.23%. The Earth-zone fraction is twelve times higher than even the closest comparison, drawn from a much smaller total. Because the baseline rate across the comparison zones is identically zero, the excess cannot be expressed as a conventional sigma. There is simply no analog population elsewhere in the inner solar system.
All 29 objects have Tisserand parameters relative to Earth tightly clustered near T_E ≈ 3.00 — a dynamical fingerprint confirming their kinship with Earth's orbit. Estimated sizes, assuming a geometric albedo of pV = 0.15, range from sub-metre to roughly 38 m. None of these sizes are measured; all are inferred from absolute magnitude.
Discussion
Three natural mechanisms can plausibly produce low-e, low-i orbits at 1 AU: capture into Earth's co-orbital resonance with prolonged circularization, lunar impact ejecta launched within a narrow velocity window, and tidal disruption of a parent body during an Earth flyby. Morais and Morbidelli (2002) predicted 0.1–10 co-orbitals at any time; 29 sits at the high end. Castro-Cisneros et al. (2023) showed that Kamo'oalewa (469219) is plausibly lunar ejecta, though most such ejecta end up at e > 0.1; the narrow ultra-circular window yields perhaps 1–3 objects, not 29. Tidal disruption would produce a clustering in orbital element space that has not been searched for rigorously and has not been reported.
The most consequential finding of this inquiry is the characterization gap. Zero of the 29 have been physically examined. No spectra, no albedos, no rotation periods, no resolved diameters. The only Earth quasi-satellite with spectral data — Kamo'oalewa — returned an S/L-type silicate spectrum consistent with space-weathered lunar material (Sharkey et al. 2021). That single data point is the extent of our present knowledge of this population's physical nature. A handful of nights at an 8-metre-class aperture would change the epistemic situation entirely. One object — 2026 AC4 — passes within 0.027 AU of Earth on 20 April 2026 at V ≈ 19.3, observable with modest instruments for roughly five weeks.
The working console
This report is the bound publication; Artifact-SETI maintains a live console with the population table, comparison zones, orbital distributions, size estimates, and observing opportunities.